Flashover preventing means for brush holder of a dynamoelectric machine



May 31, 1955 L. E. LEGG ETAL 2,709,764

FLASHOVER PREVENTING MEANS FOR BRUSH HOLDER OF A DYNAMOELECTRIC MACHINEFiled April 29, 1953 24 J tf/a/a /7 IN V EN TOR5 if, $355 5 W Ri MUnited States Patent FLASHOVER PREVENTING MEANS FOR BRUSH HOLDER OF ADYNAMOELECTRIC MACHINE Lawrence E. Legg, Chicago, and Anthony M.Scolaro, Oak Park, Ill.

Application April 29, 1953, Serial No. 351,928 3 Claims. (Cl. 310-239This invention relates, generally, to dynamoelectric machines, and ithas particular relation to means for preventing flashover between eachof the brush holders and parts of the frame of the machine at adifferent potential.

Brush holders for dynamoelectric machines, particularly those used ondiesel powered railway locomotives, are likely to flashover to adjacentparts of the machine at a different potential. This is particularlylikely to occur because of the close clearances which must exist due tospace limitations and the likelihood of entrance of dust and dirtresulting from operating under unfavorable conditions. Experienceindicates that fiashover is most likely to occur between the frame ofthe machine and that portion of the brush holder which extends beyondthe commutator and is supported by one or more 1 rigid insulators on theframe.

Accordingly, among the objects of this invention are: To preventfiashover between the brush holders of a dynamoelectric machine andadjacent portions of the frame at a different potential; to enclose thatportion of each brush holder where the fiashover is most likely to occurwith an insulating barrier; and to employ a two part insulating meansfor this purpose formed of flexible material, such as synthetic rubberparticularly neoprene.

Other objects of this invention will, in part, be obvious and in partappear hereinafter.

This invention is disclosed in the embodiment thereof shown in theaccompanying drawing and it comprises the features of construction,combination of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth and the scope ofthe application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of thisinvention, reference can be had to the following detailed description,taken together with the accompanying drawing, in which:

Figure 1 is a top plan view of a portion of a brush holder of typicaland well-known construction illustrating how the barrier of the presentinvention can be applied thereto;

Figure 2 is a view, in end elevation, looking from right to left withregard to Figure 1, certain parts of the barrier being broken away inorder to show more clearly the details of construction;

Figure 3 is a detail sectional view taken generally along the line 33 ofFigure 1; and

Figure 4 is a view showing the two part insulating means or barrier inend elevation, detached from the brush holder and shown one above theother to illustrate how they are arranged to be telescoped with respectto each other.

Referring now particularly to Figures 1, 2, and 3 of the drawings, itwill be observed that the reference character 1t) designates, generally,a brush holder of conventional construction. The brush holder 10includes a casting 11 which is formed of good conducting material,

such as brass or bronze, and having sufficient strength to withstand thestresses applied thereto. The brush holder 10 is arranged to slidablycarry brushes 12 which are arranged to engage the surface of thecommutator rotating therebelow, as will be understood readily. Thebrushes 12 are urged into contact engagement with the surface of thecommutator by brush springs 13 which are mounted on a transverselyextending rod 14. One end of the rod 14 is shown as being secured by abolt 15 to a rib 16 which is cast integrally with the casting 11. Alsocast integrally with the rib 16 is a horizontally extending web 17 whichextends underneath the springs 13. Along the sides of the web 17 arearms 18, 19, and 20 which are cast integrally therewith and with the rib16. The arms 18, 20 are formed integrally with cylindrical bosses 21which, as shown, are interconnected by a rib 23 that is integral withthe arm 19. Steel support studs 24 extend centrally through thecylindrical bosses 21 and are secured therein by transverse holdingpins, one of which is indicated at 25 in Figure 2. Also as there shown,the lower ends of the steel support studs 24 extend into porcelaininsulators 26 and are secured therein by suitable adhesive means. Theporcelain insulators 26 are carried by brass support studs 27 whichextend upwardly thereinto and are secured thereto by suitable adhesivemeans. It will be understood that the brush holder 10, just described,is of conventional construction and per se forms no part of the presentinvention.

As pointed out above, it is likely that fiashover may take place betweenthe brush holder 10 and adjacent parts of the frame of thedynamoelectric machine which are at a different potential. It isparticularly likely that the flash-over will take place between thecylindrical bosses 21 and the parts of the frame adjacent thereto atopposite potential. in accordance with this invention provision is madefor covering the bosses 21 and adjacent parts of the brush holder it) soas to avoid the likelihood of flashover.

For this purpose an insulating sleeve 30 is employed which has an upperportion 31 that, as shown in Figure 1. extends around the cylindricalbosses 21 and has end portions 32 and 33 overlying the arms 18 and 20,respectively. There is an opening 34 between the end portions 32 and 33through which the web 17 and arms 18, 19, and 20 project. As shown inFigure 4, the end portion 33 has a downwardly inclined upper edge 35.The purpose of this is to conform to the correspondingly downwardsloping of the upper edge of the arm 20. A shelf 36, formed integrallywith the upper portion 31 of the insulating sleeve 3t extends underneaththe web 17 and preferably extends far enough so that its inner edgeoverlies the adjacent ends of the commutator bars. Depending from theupper portion 31 of the insulating sleeve 30 is a bifurcated portion 37.This portion 37 comprises a pair of tubular extensions 39 which areformed integrally with r the shelf 36, and, as shown in Figures 2 and 3,are arranged to enclose the lower portions of the cylindrical bosses 21and the porcelain insulators 26. It will be understood that the tubularextensions 39 need not extend entirely over the procelain insulators 26although this is the preferred construction.

With a view to enclosing the top of the insulating sleeve 36, there isprovided an insulating cover 43. it will be observed in Figures 2, 3,and 4 that the cover 43 has a flat central portion 44 which is arrangedto overlie the upper ends of the cylindrical bosses 21 and also theupper surfaces of the arms 18, 19, and 20. An upstanding portion 45 isformed integrally with the central portion 44 and it has a slot 46therein for accommodating the upper portion 47 of the arm 18, whichextends above the level of the corresponding surfaces of the arms 19 and20 adjacent the rib 16. Formed integrally with the insulating cover 4-3is a relatively thin depending flange 48 which, as shown in Figure 3, isarranged to telescope over the upper end of the insulating sleeve 34 andto have a friction fit therewith.

The sleeve 3t) and cover 43 have been indicated and described as beingformed of insulating material. Preferably they are formed of a flexibleinsulating material, such as synthetic rubber of which neoprene is apreferred material. However, it will be understood that other similarinsulating materials can be employed. Since the insulating cover 43 isflexible, it can be deformed readily to interfit closely with thedownwardly inclined edge 35 of the end portion 33. Also because of theflexible character of the material used for the sleeve 36 and cover 43,they can closely overlie the portions of the brush holder 10 which theyare intended to cover.

For illustrative purposes, it is pointed out that the wall thickness ofthe sleeve 30 and cover 43 is about one-fourth inch. The flange 48 mayhave a thickness of about onesixteenth inch. It will be understood thatthese dimensions can be varied as the situation requires. The insulatingsleeve 30 and insulating cover 43 are molded in correspondingly shapeddies in accordance with conventional molding practice.

Since certain changes can be made in the foregoing construction anddifferent embodiments of the invention can be made without departingfrom the spirit and scope thereof, it is intended that all matters shownin the accompanying drawing and described hereinbefore shall beinterpreted as illustrative and not in a limiting sense.

What is claimed as new is:

1. Means for providing an insulating barrier enclosing one end of abrush holder having a pair of cylindrical bosses adapted to be carriedby a pair of insulators mounted on the frame of a dynamoelectric machineadjacent the commutator thereof, said bosses being joined by an integralweb and having arms extending therefrom to support the brushes, saidbarrier preventing flashover between said brush holder and portions ofsaid frame at a different potential, said means comprising, aninsulating sleeve for enclosing the outer upper portions of said bosseswith an integral depending bifurcated portion for enclosing the lowerportions of said bosses and an integral shelf underlying said arms, oneside of said sleeve being open to accommodate said arms, and aninsulating cover overlying said sleeve, said cover having 21 dependingflange overlying and coextensive with the upper periphery of saidsleeve.

2. The invention, as set forth in claim 1, wherein the sleeve and coverare formed of flexible insulating material, the flange frictionallygrips the sleeve, and the flange is thinner than the remainder of thecover.

3. The invention, as set forth in claim 2, wherein the sleeve and coverare formed of synthetic rubber.

References Cited in the file of this patent UNITED STATES PATENTS728,152 Bachelder May 12, 1903 761,985 Norris June 7, 1904 2,313,502Baldwin Mar. 9, 1943

